Journal of Geosciences, 66 (2021), 227–242

DOI: 10.3190/jgeosci.335

Original paper

Cronstedtite from Litošice, Czech RepublicJiří HYBLER1*, Zdeněk DOLNÍČEK2, Jiří SEJKORA2
Institute of Physics, Czech Academy of Sciences, Na Slovance 2, CZ-182 21 Praha 8, Czech Republic; hybler@fzu.cz
Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, CZ-193 00 Praha 9, Czech Republic*
Corresponding author
1
2

The layered iron silicate cronstedtite was encountered in ore veins in the exploration shaft mined in the Neoproterozoic
black shale-hosted pyrite-manganese deposit near Litošice (Eastern Bohemia, Czech Republic) around 1955. It forms up
to 2 mm thick black double or single bands in symmetrically zoned hydrothermal veins cutting shales. The specimens
selected from available material were studied by single-crystal X-ray diffraction using the four-circle diffractometer withan area detector. The chemical composition of some of the specimens was determined by the electron probe microanalysis(EPMA) in the WDS mode. Furthermore, a polished section of the ore material with cronstedtite bands was prepared,
and the mineral association was analyzed with the aid of back-scattered electron (BSE) images. The interpretation ofreciprocal space (RS) sections produced by the diffractometer software allowed the determination of OD subfamilies(Bailey’s groups) A, B, C, D, and polytypes. The 1T polytype (subfamily C), a = 5.52, c = 7.12 Å, space group P31m, isthe most abundant in the occurrence. In rare cases, it forms oriented crystal associations (allotwins) with the 1M polytype(subfamily A), a = 5.52 Å, b = 9.55, c = 7.136 Å, β = 104.4°, space group Cm. Fully disordered allotwinned crystals of
the A + C subfamilies were found, too. In addition, few allotwins of the polytype 2H1 (subfamily D) with a small amountof 2H2, were identified. Unit cell parameters are a = 5.49, c = 14.21 Å, space groups are P63cm (2H1), and P63 (2H2).
EPMA-WDS of selected crystals of prevailing 1T polytype revealed elevated contents of Mn (0.19–0.62 apfu) and low
contents of Mg (up to 0.13 apfu) and Cl (up to 0.05 apfu), respectively. More rare 2H1 (+ 2H2) polytypes show elevatedcontents of Mg in the range of 0.19–0.62 apfu and distinctly lower Mn (up to 0.07 apfu) and Cl contents (up to 0.01 apfu).
The BSE images reveal that cronstedtite bands are associated with multiple generations of carbonates (rhodochrosite,siderite, rarely magnesite and calcite), quartz, opal, pyrite and carbonate-fluorapatite. Intense metasomatic replacementof cronstedtite by opal and siderite appeared especially around the center of the studied vein.
Keywords: Cronstedtite, 1 : 1 layered silicate, polytypism, stacking disorder, allotwinning
Received: 30 July 2021; accepted: 9 December 2021; handling editor: J. Kotková
The online version of this article (doi: 10.3190/jgeosci.335) contains supplementary electronic material.

1. Introduction
The layered silicate cronstedtite is ‘Grandfathered’mineral
first described by Steinmann (1820, 1821) from theVojtěch Mine in Příbram, and named in honor of theSwedish chemist and mineralogist Axel Fredrik Cronstedt (*23. 12. 1722, †19. 8. 1765). It was subsequently
described from Rejské Lode in the Kaňk part of the Kutná
Hora ore district by Vrba (1886), and more recently by
Novák et al. (1957). Other occurrences reported in the
Czech Republic are Chvaletice (Novák and Jansa 1965;
Hybler 1998), Pohled Quarry near Havlíčkův Brod
(Hybler et al. 2016), Chyňava (Fiala 1951; Fiala andKouřimský 1980; Hybler and Sejkora 2017), and Litošice(Novák and Hoffman 1956; Hybler 1998, this study).
Several other occurrences in Central Europe were also
reported: Rožňava (Varček et al. 1990), Nižná Slaná (Hybler et al. 2017) in Slovakia, Nagybörzsöny in Hungary(Hybler et al. 2020), and Lutherstadt Eisleben in Germany (Hybler 2014). Generally, cronstedtite is a scarcemineral, as it was usually found in a limited amount and/or in a limited time window. Some occurrences are quite
unique – like a piece of a drill core from the Chyňava
borehole, or a few pieces of the ore material found ina veinlet in the Pohled Quarry, quickly removed by acontinuing excavation.
Cronstedtite typically occurs in low- and medium temperature hydrothermal veins together with quartz, calcite,
in some cases with siderite, ankerite, rhodochrosite, and/or rhodonite, but always with pyrite – on the surface,in cavities, druses, inter-grown, in veinlets, or embedded in the polycrystalline mass or weathering products(e.g., Hybler et al. 2016, 2017). It has also been foundin metamorphic banded iron formations (Gole 1980a, b;
López-García et al. 1992), and in some meteorites, suchas CM chondrites (e.g., Müller et al. 1979; Barber 1981;
Burbine and Burns 1994; Browning et al. 1996; Lauretta
et al. 2000; Zega and Buseck 2003; Schulte and Schock2004; Dyl et al. 2010; Pignatelli et al. 2016, 2017, 2018).
Spectroscopic data suggest that cronstedtite might bepresent in extraterrestrial environments, such as certain
dark regions of Mars (Calvin 1998) and on the dwarf
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Jiří Hybler, Zdeněk Dolníček, Jiří Sejkora

planet Ceres (Zolotov 2014). Pignatelli et al. (2013,2020) repeatedly synthetized micrometer-sized crystalsof cronstedtite by an iron–clay reaction at 60–90 °C.
Samples from these syntheses were later studied by Hybler et al. (2018) by electron diffraction.
Cronstedtite belongs to 1 : 1 phyllosilicates of theserpentine–kaolinite group (Steadman and Nuttall 1963,
1964; Steadman 1964). Its structural formula is (Fe2+3–x
Fe3+x)(Si2–xFe3+x)O5(OH)4, where x is usually in the rangeof 0.5 to 0.85. The structure is composed of edge-sharing
octahedral and adjacent corner-sharing tetrahedral sheets,
forming together 1 : 1 layer (Bailey 1988). Octahedral
positions are occupied by Fe2+ and Fe3+, while Si4+ ispartially substituted by Fe3+in tetrahedral positions. Presumably, the proportion of Fe 3+ in octahedra balances
the charge deficiency in tetrahedra. Moreover, a partial
substitution of Fe2+ in octahedra for Mn2+ and/or Mg2+ has
been reported in cronstedtite from some occurrences, e.g.,Příbram (Steinmann 1821; Damour 1860; Janovský 1875;
Geiger et al. 1983), Chyňava and Ouedi Beht, Morocco(Hybler and Sejkora 2017; Hybler et al. 2021). The Mnrich analog of cronstedtite described from South Africa
was approved as a new distinct mineral species guidottiite(Wahle et al. 2010).
The 1 : 1 layer silicates, including cronstedtite are typical representatives of Order-Disorder structures of layers(OD structures in the following text) with a low degree ofdesymmetrization (Dornberger-Schiff and Ďurovič 1975a,b; Ďurovič 1981, 2004). They belong to the OD family,
subdivided into four OD subfamilies according to shifts
and/or rotations of consecutive (identical) layers. These
subfamilies are identical to Bailey’s (1969, 1988) groups:
A (polytypes 1M, 2M1, 3T, 6T2), B (2O, 2M2, 6H), C (1T,
3R, 2T) and D (2H1, 6R1, 2H2). The stacking rules are
represented by the following operations: ± ai/3 shifts for
subfamily A, ± ai/3 shifts combined with 180º rotation
for subfamily B, ± b/3 or no shift for subfamily C, ± b/3
or no shift combined with 180º rotation for subfamily
D, where ai, b correspond to the vectors of trigonal andorthohexagonal cells, respectively. Such variability oflayer stacking gives rise to a relatively high amount ofpolytypes.
Groups and polytypes are identified with the aid ofcharacteristic single-crystal X-ray diffraction patterns,
Selected Area Electron Diffraction (SAED), and Electron Diffraction Tomography (EDT). The X-ray powder
diffraction is not reliable in many cases for the polytype
determination (Ďurovič 1997).
Existing single-crystal diffraction data for several
cronstedtite samples from Litošice using the precession
camera resulted in the identification of only 1T polytype(Hybler 1998). Later studies of cronstedtite from otherlocalities (Hybler and Sejkora 2017; Hybler et al. 2016,2017, 2020) manifested the necessity of checking a228

large number of specimens (tens or even hundreds) bysingle-crystal X-ray diffraction in order to reveal possible variability.
The aim of this study is to provide detailed data on
the mineral cronstedtite using samples stored in the National Museum, Prague, which have become available
for research. In particular, it focuses on testing more
specimens for polytypism, twinning, allotwinning andstacking disorder, which might be present within one
occurrence, along with the determination of the chemicalcomposition, paragenesis and relations to other minerals
in the assemblage.

2. Occurrence

2.1. Geology
Neoproterozoic stratiform Mn-carbonate and pyrite
mineralization of “black shales” occurs in a disjunctively disturbed synclinorium in the Chvaletice–Zdechovice–Morašice–Litošice–Sovolusky belt in the Železnéhory, Proterozoic Unit (Central/Eastern Bohemia, Czech
Republic). The mineralization has been interpreted asa product of submarine volcanic activity and is partly
affected (especially in the SE part) by metamorphic
processes (Bernard 1991). The prevailing stratiform ore
mineralization is accompanied by younger veins with ahigh content of Mn. The Fe and Mn ores were mined ona small scale in this area from the Middle Ages, and themain deposit Chvaletice was exploited as a source of
pyrite for the chemical industry by a large open-pit minein 1951–1975. More than 30 million tons of pyrite ores
were produced (Bernard 1991).

2.2. Mining history and mineralogy
Litošice is a small village on the boundary of Central andEastern Bohemia, about 7 km SSW of Přelouč, 20 km SW
of Pardubice. The approximately 500 m wide ore zone
strikes in NW–SE direction, starting 1 km W of Litošiceand terminating 0.5 km SW of Sovolusky. It is largely
covered by forest except for its SE margin. This zone
represents a southeastern continuation of the Chvaletice
deposit.
In the study of Slavík (1928) and unpublished research reports of Kempný et al. (1955) and Bartas(1960), the mining activities were reported south of theroad Litošice–Žehušice, i.e., 1.2 km W of Litošice, in
1916–1917, 1919 and 1930. The 53 m deep shaft withfour levels and numerous adits was opened in 1919 or
1920 by the Prague Iron Company in this area. Moreover,remnants of even older mining activity (depressions,slumps) were apparent nearby, too. They were probably

Cronstedtite from Litošice

excavated for “limonite” from a gossan since the Middle
Ages. Slavík (1928) also reported two quarries near Sovolusky and Morašice opened in 1926 and 1927. Bartas(1960) mentioned two smaller shafts SW from Sovolusky,
18 m and 11 m deep, respectively. All these workings
were exploited for the manganese ores. Following minerals were reported in the study of Slavík (1928) for the
Litošice area: pyrite, pyrrhotite, garnet, amphibole asbestos, arsenopyrite, chalcopyrite, quartz (colorless or in
the form of amethyst), manganite, hausmannite, calcite,rhodochrosite, siderite, alunite, destinezite, aluminite,delvauxite, vivianite, vashegyite, anthophyllite, and alone
curious discovery of anthracite. The genesis of Litošiceand other deposits in the area was described by Slavík(1929). In the 1950s, an extensive geological exploration
for pyrite mineralization in black shales was performed.
These workings, geological mapping and drilling, werecarried out from 1952 by the Central Geological Institute(Ústřední Ústav Geologický), Prague. From 1954, theCzech–Moravian Ore Research (Českomoravský rudníprůzkum), Kutná Hora continued in explorations by boring of denser network of boreholes and digging of shafts
10, 11, 13, 14, 15, 16. While only short galleries were
driven from the shafts 13, 14, 15, extensive networksof adits on two levels were advanced from the shafts
10, 11 and 16. The aim of these explorations was theverification of reserves of pyrite shales in the deposit for
the exploitation planned after the closure of the nearby
Chvaletice quarry. Several reports of these exploration
works are stored in the Czech Geological Survey – Geofond, Prague: Bartas (1955, 1960), Kempný et al. (1955),
Fiala and Svoboda (1953, 1956), Papoušek (1956a, b,1957). The reports of Bartas (1955, 1960) are the mostcomprehensive, containing numerous drilling profiles aswell as the geological map of adits dug on two levels (at50 and 100 m depth) from shaft No. 10. The entire geological profile of excavation of shaft No. 10 is included in
the report of Kempný et al. (1955). A rhodochrosite veinin the depth of 41–45 m, 50 cm thick, striking NW–SE
and dipping 58–66° to NE was encountered during the
digging of the shaft. Bartas (1960) reported two rhodochrosite veins encountered in the heading denoted as 101(depth 50 m), in direction SE 1–3 m and 18–20 m far
from the shaft, respectively. Another thin rhodochrosite
vein was also observed at cross adits denoted as 1001 and1002 around the shaft.
Since pyrite used for the production of sulfuric acidwas gradually replaced by the import of native sulfur
from Poland since the late ’50s, the deposit was never
exploited and remained as a reserve. At present, theshafts are abandoned, filled up with formerly excavatedmaterial and remains of dismantled dumps. Žák (1955)
studied material from the shaft (as stated in the study)
1200 m S of Litošice, evidently corresponding to shaft

No. 10. He explored material from the ore vein at a depthof 41–45 m. Alabandite (2 generations), accompanied byother minerals: rhodochrosite (4 generations), neotokite,pyrite, ankerite, quartz, chalcedony, was reported. No
cronstedtite was reported.
Novák and Hoffman (1956) described several minerals from the material collected in the area. They also
explored a dump of the shaft near Sovolusky (as they reported) – evidently of shaft No 10. The authors describedsamples with symmetrical bands of black cronstedtiteof the thickness up to 5 mm along with carbonate–rhodochrosite vein with quartz in the center. Qualitative
spectral and wet chemical analyses revealed a certain
content of Mn. However, they attributed it to a possible
admixture of rhodochrosite. The powder diffraction data
were reported and compared with data of cronstedtite
from Kutná Hora and Cornwall. No attempt to perform
single-crystal studies was made. Other minerals reported
from this shaft are opal, alabandite, neotokite, and pyrite.
Cronstedtite was later recognized in the material collected by Lubor Žák (LŽ) in 1955, originating from theshaft No. 10, the ore vein at a depth of 41–45 m (LŽ,priv. comm.). Hybler (1998) presented the first preliminary single-crystal diffraction study of cronstedtite from
Litošice (obtained directly from LŽ) and nearby Chvaletice using the precession camera. He identified nothing
but the 1T polytype in a few samples from Litošice hestudied at that time.

3. Samples
Small fragments of ore material provided by LŽ to thefirst author of this paper (JH), and several compact piecesof carbonate veins with bands of cronstedtite stored in
the collection of the National Museum were used for thisstudy. All samples with their catalog numbers, donators,
and brief characteristics are reported in Tab. 1. With one
exception, all of them evidently originated from the shaft
No. 10 (GPS 49°58’23.8“N, 15°30’38.7“E); however,
the reported localities are distinct – Litošice, Sovolusky,Semtěš, and Vápenka. The reason for this ambiguity,also found in the studies cited above, is the location of
the shaft at comparable distances from given villages andplaces. However, shaft No. 10 is located in the cadastralarea of Litošice. Thus this name is used for the locality
in the following text.
Note that two samples donated by LŽ (P1N 111848
and P1N 111849), collected in 1955, are explicitly attributed to shaft No. 10, depth of 47 m. The sample
P1N 111848 is presented in Fig. 1. The other two welllocalized samples came from the same shaft, depth of
50 m, first head (P1N 66872) or E–W-trending crossadit 15 m from the shaft (P1N 74127). The relationship229

Jiří Hybler, Zdeněk Dolníček, Jiří Sejkora

Fig. 1 Ore vein with symmetrically arranged black double bands of cronstedtite. National Museum, Prague, catalog
number P1N 111848. Photo P. Škácha.

between these occurrences around shaft No. 10 cannot
be assessed. Cronstedtite usually forms double, rarely
single bands about 5 mm thick, symmetrically locatedon both sides of the core of the vein, composed of opal
and Fe–Mn carbonates. It is black colored, with vitreous
luster and with perfect {001} cleavage.
The last listed sample is originally from the collection of Karel Paděra cat. No. P1N82054 is initially labeled as Morašice. The sample’s appearance and othercharacteristics (polytypes, chemical compositions) aresimilar to the other samples. However, the given village isrelatively far from shaft No. 10 (3.2 km). Thus the sample
possibly comes from another locality. In the proximity of
Morašice, two mining works are referred to in the Czech
Geological Survey – Geofond: an old, pre-1945 adit
(49°59’51.5“N, 15°29’10.3“E), and a post-WWII shaft

No. 52 (50°00’25.9“N, 15°28’36.6“E). Nevertheless, we assume that the described sample comes from Litošice, too, as
this ore district was previously referred to as Zdechovice–
Morašice (Bernard et al. 1981), and localization of samples
from the Paděra’s collection is often not too accurate.

4. Experimental techniques
Crystals were separated from bands in the given samples
and under the stereomicroscope. The typical size of
specimens was 0.05–0.2 mm. Separated fragments werelabeled according to the catalog numbers of samples, likeP1N40571-1, P1N40571-2, etc. In the case of the P1N
111848 sample, several batches of fragments were takenfrom individual sequentially labeled bands, with two

Tab. 1 List of samples used for the study.
Origin*
LZ
NM
NM
NM

Catalogue
NumberLocality quoted

Donated by

Litošice – shaft No. 10, dump
Lubor Žák, personally to JH
Litošice – shaft No. 10
Lubor ŽákSovolusky – shaft No. 10
Vl. Hofman, Kutná Hora
Litošice
J. Hora, Prague
VápenkanearSemtěš
–
shaft
No.
10,
NM
P1N 66872 carbonate vein on the 1. heading
P. Povondra, Prague– "Na vápence", shaft No. 10, J. V. Frič, Prague
NM
P1N 74127 Semtěš
E-W cross adit 15 m from the shaft– Vápenka, shaft No. 10,
Lubor Žák, Prague
NM
P1N 111848 Litošice
depth 47 m, 1200 m S from Litošice (in 2006, collected 1955)– Vápenka, shaft No. 10,
Lubor Žák, Prague
NM
P1N 111849 Litošice
depth 47 m, 1200 m S from Litošice (in 2006, collected 1955)
NM
P1N 82054 Morašice
Karel Paděra, Prague* LZ – obtained directly from Lubor Žák; NM – collection of the National Museum, Prague

230

P1N 40571
P1N 52382
P1N 60314

fragments
bands in carbonate veinbands in carbonate veinbands in carbonate vein

Fragments
studied46
18
35
6

bands in carbonate vein

9bands in carbonate vein

23

bands in carbonate vein

35

bands in carbonate veinnone

bands in carbonate vein

24

Form

Cronstedtite from Litošice

batches representing two domains of band 3. The batches
were thus labeled as P1N111848-V1, P1N111848-V2,
P1N111848-V3H, P1N111848-V3S, and P1N111848-V4.
All fragments were glued onto the glass fibers. They werestudied by X-ray diffraction and some of them were afterward used for the electron probe microanalysis (EPMA).

collection, unit cell parameters calculation, and processing of data recorded. A total of 196 specimens were
tested. Some of them were later cleaved into smaller
fragments, which were studied separately. About 380
frames were recorded during special pre-experiments and
500–600 frames during full experiments. The “unwarp”
procedure created user-defined images of reciprocal
space sections (RS sections in the following), which areequivalents of precession photographs.
The RS sections corresponding to six important
reciprocal lattice planes were generated: (2hh̄l hex)*,(hhl hex)*, (h̄2hl hex)*, (h0l hex)*, (0kl hex)*, and (h̄hl hex)*.
Distributions of so-called subfamily reflections along thereciprocal lattice rows [21̄l]* / [11l]* / [1̄2l]* in (2hh̄lhex)*/ (hhl hex)* / (h̄2hl hex)* planes, respectively, are used todetermine OD subfamilies (Bailey’s groups) A, B, C, D
(Dornberger-Schiff and Ďurovič 1975a, b; Bailey 1969;1988). Similarly, distributions of characteristic reflections
along [10l]* / [01l]* / [1̄1l]* rows in (h0lhex)* / (0klhex)* /(h̄hlhex) RS sections were used to determine polytypes.
Graphical identification diagrams for a simple visualcomparison with real diffraction patterns were used.
They were already published elsewhere (Mikloš 1975;Ďurovič 1981, 1997; Weiss and Kužvart 2005; Hybler et
al. 2018, 2021). Unit cell parameters of selected samples
are summarized in Tab. 2. For some specimens, the full

4.1. Single crystal X-ray diffraction
Selected crystal fragments were studied by the singlecrystal X-ray diffraction with the aid of the four-circle(double-wavelength) X-ray diffractometer Gemini A
Ultra (Rigaku Oxford Diffraction) equipped with the
CCD area detector Atlas S2 at the Institute of Physics,
Czech Academy of Sciences. The MoKα radiation, withgraphite monochromator, λ = 0.71070 Å, and Mo-enhance fiber optics collimator were used. At the beginningof the study, special pre-experiments were performed
covering a sufficiently large portion of the reciprocal
space. Later the strategy was changed: the quick preexperiment was performed first, followed by a complete
experiment with limited parameters (mainly exposuretime), but always covering the whole sphere. Such an
experiment typically required tens of minutes or several hours. The CrysAlisPro version 171.41.93a (Rigaku
Oxford Diffraction 2021) package was used for the data

Tab. 2 Unit-cell parameters (in Å, degrees, with standard uncertainties – s.u.‘s in parentheses), subfamilies (Bailey’s groups), and polytypes of
selected crystals of cronstedtite from Litošice.
SampleNote
Disordered, diffuse streaks, cell parameters
LZ-12-2
5.5162(6)5.5162(6)21.334(2)562.19(11) C+A disorderedof the subfamily A structure, Fig. 5LZ-14
5.5290(12)5.5290(12)7.1262(15) 188.66(7)C
Diffusely streaked, EPMA
1T
LZ-23
5.5262(12)5.5262(12)7.124(2)188.40(9)C
Diffusely streaked, EPMA
1T
Allotwin, diffusely streaked, cell
LZ-27
5.5264(16)5.5264(16)7.151(3)189.15(12) C+A
1T+1M
parameters 1T polytype5.5166(11) 9.5546(17); 104.44(2) 7.3585(17) 375.62(13) C+A
1T+1M Cell parameters 1M polytype, Fig. 4
LZ-40
5.5263(13)5.5263(13)7.1288(18) 188.54(8)C
Diffuse streaks, EPMA
1T
Diffuse streaks, parasitic misoriented
LZ-41
5.5200(12)5.5200(12)7.119(2)187.86(8)C
1T
crystals, EPMA
LZ-44
5.5181(15)5.5181(15)7.127(2)187.94(9) C(+A?)
Subfamily A reflections weak, EPMA
1T
Char refl. weak, smeared, diffuse streaks,
P1N 40571-3
5.529(2)5.529(2)7.182(4)190.16(15)
C
1T
EPMA
Allotwin, strong 2H1, weak 2H2 reflections,P1N 40571-9
5.4942(5)5.4942(5)14.2146(13) 371.60(6)D
2H1+(2H2)
diffuse streaks, EPMA, Fig. 3
P1N 40571-13
5.5211(8)5.5211(8)7.1368(12) 188.40(5)C
Diffuse streaks, EPMA, Fig. 2
1T
Poor crystal, char. refl. weak, diffuse
P1N 60314-2
5.552(5)5.552(5)7.069(9)188.9(3)C
1T
streaks, EPMA
Char. refl. weak, diffuse streaks, Debye
P1N 60314-4
5.545(2)5.545(2)7.130(2)189.89(13)C
1T
arcs, EPMA
Characteristic reflections strong, diffuse
P1N 60314-6
5.5195(9)5.5195(9)7.1292(14 188.09(6)C
1T
streaks
Characteristic reflections strong, diffuse
P1N 74127-9
5.5248(9)5.5248(9)7.1444(16) 188.86(6)C
1T
streaks
Characteristic reflections strong, diffuse
P1N 111848-V2-3 5.5176(10)5.5176(10)7.1233(16) 187.81(6)C
1T
streaks, Debye arcs, EPMA
Average cryst., char. refl. aver., diffuse
P1N 111848-V4-6 5.5170(6)5.5170(6)7.1377(10) 188.15(4)C
1T
streaks, Debye arcs, EPMA
P1N 82054-1
5.516(2)5.516(2)7.137(4)188.06(15)C
Reportedly from Morašice? EPMA
1T
EPMA – sample selected for EPMA, LZ – samples from Lubor Žák, other samples from National Museum
a

b; β

c

V

Group Polytype(s)231Jiří Hybler, Zdeněk Dolníček, Jiří Sejkora

Fig. 2 RS sections – equivalents of precession photographs of the polytype 1T.
Indices of reciprocal lattice rows and of
selected reflections, as well as reciprocallattice vectors are indicated where possible. Auxiliary horizontal lines passing
through the origins of sections are added
to aid the eye in all RS section images
presented in this study. a – The (hhlhex)*
section. The reflections of [11l]*, and symmetry equivalent [1̄1̄l]*, reciprocal latticerows are at the same levels as reflectionsof the [00l]* row. This arrangement ischaracteristic for the subfamily C. b – The(h0lhex)* section with characteristic reflections [10l]* and [1̄0l]*, also at the samelevel as reflections of the [00l]* row, characteristic for the 1T polytype. The same
is valid also for second-order characteristicrows [20l]* and [2̄0l]*. Note smeared anddiffusely streaked characteristic reflections
due to partial stacking disorder. Specimen
P1N 40571-13.

experiment was repeated with modified parameters inorder to obtain more precise and less noisy RS sections
for the publication.

4.2. Electron probe microanalysis
The selected fragments of cronstedtite crystals (30 fragments from 8 samples), in which polytypes were determined, were mounted in epoxy discs and polished bydiamond suspensions. In addition, one polished section
was prepared from a slab taken from the bulk vein withcronstedtite bands of the sample P1N74127 to assess
the whole mineral paragenesis. After inspection undera polarizing microscope, samples were coated with acarbon layer of about 30 nm in thickness and analyzed
at the National Museum in Prague, using a CAMECASX-100 electron probe microanalyzer. Identificationof minerals based on rapid energy-dispersive spectra(EDS) was followed by quantitative measurementsof chemical composition of selected phases in the
wavelength-dispersive (WDS) mode with an acceleration voltage of 15 kV, beam current of 10 nA (apatite,cronstedtite) or 5 nA (carbonates) and beam diameterof 5 µm. The following elements were analyzed inindividual mineral phases: cronstedtite: Al, Ca, Cl, F,
Fe, K, Mg, Mn, Na, P, S, Si, Zn; carbonates and SiO2
minerals: Al, Ba, Ca, Co, Fe, Mg, Mn, Na, Ni, P, S,
Si, Sr, Zn; apatite: Al, As, Ba, Ca, Ce, Cl, F, Fe, K,
Mg, Mn, Na, P, Pb, S, Si, Sr, Y and Zn. The following
standards and analytical lines were used: albite (NaKα),baryte (BaLα), CePO4 (CeLα), Co (CoKα), chalcopyrite(CuK α), clinoclase (AsL β), fluorapatite (CaK α, PK α),celestite (SrL β, SK α), diopside (MgK α), halite (ClK α),
hematite (FeK α ), LiF (FK α ), Ni (NiK α ), rhodonite232(MnKα), sanidine (KKα, SiKα, AlKα), vanadinite (PbMα),wollastonite (CaKα), YVO4 (YLα) and ZnO (ZnKα). The
peak counting times were between 10 and 20 s and halfof the peak time was used for both background positions. The raw counts were converted to wt. % using thestandard PAP procedure (Pouchou and Pichoir 1985).
Automatic correction of overlap CaKβ - PKα in carbonate analyses was applied. Oxygen was calculated fromstoichiometry. The above-listed elements, which are
not included in the tables of primary data (Tabs S1–S3,
ESM) were in all cases below the limits of detection.
The contents of H2O, Fe2+ and Fe3+, as well as x-values,
were calculated on the basis of the general formula ofcronstedtite (Fe 2+3–x Fe3+x)(Si2–xFe3+x)O5(OH)4.

5. Results and discussion

5.1. Polytypes foundCronstedtite crystals from Litošice belong mostly to the
1T polytype. Unit cell parameters are a = 5.52, c = 7.12
Å, space group is P31m. It is the simplest polytype of thesubfamily (Bailey’s group) C, as it is built by the mere
stacking of layers without any shift. This polytype isubiquitous in all samples studied as well as in all bands.
Almost all crystals exhibit partial stacking disorder. The
characteristic reflections on RS sections are smeared, anddiffuse streaks along reciprocal lattice rows are present.
Well-ordered crystals providing sharp characteristic reflections are rare. Typical RS sections of partially disordered 1T polytype are presented in Fig. 2.
The polytype 2H1 (subfamily D) was identified in two
crystals from the sample P1N 40571. Both crystals also

Cronstedtite from Litošice

Fig. 3 RS sections of the polytype 2H1,
with a small amount of the polytype
2H2, in fact, 2H1+2H2 allotwin. Selectedreflections are indexed and reciprocallattice vectors are indicated when possible. a – The (hhlhex)* section, with reflections for the subfamily D in [11l]*,and [1̄1̄l]* reciprocal lattice rows. Theirperiodicity is the half of [00l]* row,which means doubled periodicity inthe direct space due to regular alternations of layers rotated by 180°. b – The(h0lhex)* section. Strong characteristicreflections [10l]* and [1̄0l]* have thesame periodicity as these of the [00l]*
row, because the l = 2n + 1 reflections
are absent due to systematic absencesof the space group P63cm. The weakl = 2n + 1 reflections belong to the polytype 2H2, space group P63. Specimen
P1N 40571-9.

contain a small amount of the polytype 2H2. For this kindof oriented crystal association of polytypes Nespolo et al.
(1999) proposed the term allotwin. Unit cell parameters
are a = 5.49, c = 14.21 Å, space groups are P63cm (2H1),
and P63 (2H2). The respective RS sections of one of suchallotwins are shown in Fig. 3. The second selected specimen is very poorly crystalline.
Several rare crystals in the occurrence produced complex diffraction patterns containing the reflections of thesubfamilies C and A. Moreover, in diffraction patterns ofsome of these crystals, the reflections of 1T as well as of
the 1M polytypes were found. These crystals represent
other examples of allotwins. While the 1T polytype iscommon in the occurrence, the 1M polytype (a = 5.52
Å, b = 9.55, c = 7.136 Å, β = 104.4°, space group Cm),belonging to the A subfamily was identified only in several specimens, and always as components of allotwins.
Representative RS sections are presented in Fig. 4.
The reciprocal lattice rows [21̄l]* / [11l]* / [1̄2l]* in(2hh̄lhex)* / (hhlhex)* / (h̄2hlhex)* planes (Fig. 4a) reveal superposition of reflections of the A group (shifted by +1/3
or –1/3 of the periodicity of reflections of the [00l]* row),and of the C group (with reflections at the same level asin the [00l]* row). One of (h0lhex)* / (0klhex)* / (h̄hlhex)*
RS sections reveal characteristic reflections at the levelof reflections of the [00l]* row. However, they containa contribution of the 1T polytype, and that of the plane
perpendicular to the symmetry plane (m) of the 1M polytype, i.e., the (h0lmon)* RS section (Fig. 4d). The characteristic reflections of both polytypes overlap. In other
RS sections of this kind, reflections of both polytypes are
separated; while the 1T polytype reflections are still inthe same positions, the 1M polytype reflections belonging to the plane diagonal to the symmetry plane (m) areshifted by 1/3 or –1/3 of the periodicity of the [00l]* row(Fig. 4b–c). A similar allotwinned 1T + 1M (A + C) crystal
was identified by electron diffraction in the synthetic run
product (Hybler et al. 2018) and in a meteorite – Cochabamba carbonaceous chondrite (Müller et al. 1979).
RS sections of isolated polytype 1M were published by
Pignatelli et al. (2013), Hybler (2014), and Hybler et al.
(2018, 2020). While the 1M polytype is generally rare,
the much more abundant polytype 3T from subfamily A
was not identified in the studied samples.
Several A + C allotwinned crystals are entirely disordered. Diffraction patterns of one of such crystals are presented in Fig. 5. The rows of characteristic reflections are
replaced by diffuse streaks due to the stacking disorder.

5.2. Chemical composition of cronstedite
In order to examine compositional variability of the studied cronstedtite polytypes, a total of 235 spot analyses
from thirty selected fragments and 66 spot analyses froma polished section of sample P1N74127 with cronstedtite
bands were collected. The complete data set of analyses
is given in Tab. S1 (ESM). The BSE imaging suggests
the compositional homogeneity of all studied fragmentsof cronstedtite crystals.
For a predominant 1T polytype, the calculated xvalues in the general formula range between 0.69 and0.86 (Tab. 3), and samples show characteristic elevatedcontents of Mn in the range of 0.19–0.62 apfu (Fig. 6a),while the contents of Mg are distinctly lower and do not
exceed 0.13 apfu (Fig. 6b). The presence of Mn and/or Mg partially replacing Fe2+ in octahedra has been reported from some occurrences, e. g. Příbram (Steinmann
1821; Geiger et al. 1983), Chyňava (Hybler and Sejkora233Jiří Hybler, Zdeněk Dolníček, Jiří Sejkora

Fig. 4 RS sections of the rare allotwinned crystal of polytypes 1T and 1M of subfamilies C and A, respectively. Reciprocal lattice vectors areindicated where possible. (a*h , b*h c*h are hexagonal reciprocal vectors, a*m , b*m c*m are monoclinic reciprocal vectors). a – The superposition of(hhlhex)* and (h0lmon)* RS sections 1T and 1M polytypes, respectively. The reflections of the subfamily C in [11l]* and [1̄1̄l]* rows (black indices)
are at the same level as reflections of the of [00l]* row, while the reflections of the subfamily A in [20l]* and [2̄0l]* rows (red indices) are shiftedby 1/3 c* c or –1/3 c*. b, c – Superposition of the (h̄hlmon)* and (hhlmon)* RS sections, respectively, of the reciprocal lattice of the 1M polytype
diagonal to the plane of symmetry and (h0lhex)* and (0klhex)* sections, respectively, of the 1T polytype. The characteristic reflections of the 1T polytype (black indices) are at the same level as reflections of the [00l]* row, while the characteristic reflections of the 1M polytype (red indices) areshifted by 1/3 c* c or –1/3 c*. d – Superposition of the RS section (0klmon)* of the reciprocal lattice of the 1M polytype perpendicular to the planeof symmetry and (h̄hlhex)* section of the 1T polytype. In this case, reflections of both polytypes are at the same level as reflections of the [00l]*
row, and they thus overlap. Note also diffuse streaks along the rows of characteristic reflections due to partial stacking disorder and arc-shaped
subfamily reflections due to poor crystallinity of the sample studied. Specimen LZ-27.

234

Cronstedtite from Litošice

Fig. 5 RS sections of the rare disordered allotwinned crystal of subfamilies C and A. a – The (hhlhex)* RS section with reflections of C and A
subfamilies like in Fig. 4a. b – The (h0lhex)* section, with diffuse streaks instead of the characteristic reflections due to the stacking disorder.
Specimen LZ-12-2.

2017) or Ouedi Beht, Morocco (Hybler et al. 2021). The
Mn-analogue of cronstedtite, guidottiite, was describedby Wahle et al. (2010) from ’N’Chwaning Mines, South

Africa. The elevated contents of Cl in the range 0.02–0.05
apfu were also determined in the studied samples; these
Cl contents are negatively correlated with Mn (Fig. 6c).

Fig. 6 Chemical composition of cronstedtite from Litošice: a – x-value
vs. Mn (apfu). b – Mn vs. Mg (apfu). c – Mn vs. Cl (apfu) plots.

235Jiří Hybler, Zdeněk Dolníček, Jiří Sejkora

Tab. 3 Chemical composition of cronstedtite from Litošice (apfu).
sampleLZ

polytype
1T

mean
min
max

Fe2+
1.774
1.698
1.889

Mg
0.006
0.000
0.036

Mn
0.438
0.393
0.493

Al
0.001
0.000
0.010

Fe3+
1.564
1.426
1.653

Si
1.217
1.174
1.282

S
0.002
0.000
0.006

Cl
0.024
0.018
0.030

OH
3.974
3.966
3.982

x-value
0.78
0.72
0.83

P1N 111848

1T

mean
min
max

1.847
1.678
1.985

0.008
0.000
0.046

0.345
0.219
0.484

0.002
0.000
0.025

1.599
1.486
1.708

1.200
1.146
1.257

0.003
0.000
0.006

0.033
0.017
0.053

3.964
3.942
3.982

0.80
0.74
0.85

P1N 40571

1T

mean
min
max

1.887
1.801
1.977

0.006
0.000
0.034

0.319
0.270
0.350

0.002
0.000
0.015

1.576
1.396
1.677

1.211
1.162
1.302

0.003
0.000
0.005

0.034
0.026
0.044

3.963
3.954
3.972

0.79
0.70
0.84

P1N 52382

1T

mean
min
max

1.788
1.674
1.899

0.007
0.000
0.018

0.396
0.298
0.502

0.002
0.000
0.012

1.617
1.557
1.650

1.191
1.175
1.221

0.002
0.000
0.004

0.032
0.025
0.039

3.966
3.958
3.975

0.81
0.78
0.83

P1N 60314

1T

mean
min
max

1.732
1.587
1.819

0.013
0.000
0.039

0.492
0.393
0.617

0.008
0.000
0.037

1.518
1.422
1.617

1.237
1.188
1.283

0.002
0.000
0.004

0.024
0.018
0.032

3.975
3.964
3.982

0.76
0.72
0.81

P1N 66872

1T

mean
min
max

1.753
1.717
1.806

0.007
0.000
0.023

0.454
0.438
0.461

0.003
0.000
0.014

1.568
1.489
1.643

1.214
1.174
1.255

0.002
0.000
0.004

0.025
0.021
0.029

3.973
3.969
3.977

0.79
0.74
0.83

P1N 74127

1T

mean
min
max

1.845
1.686
1.948

0.003
0.000
0.031

0.356
0.282
0.486

0.001
0.000
0.014

1.590
1.481
1.719

1.204
1.141
1.259

0.003
0.000
0.006

0.035
0.022
0.046

3.963
3.952
3.976

0.80
0.74
0.86

P1N 74127 (PS)

1T

mean
min
max

1.811
1.640
2.084

0.027
0.000
0.131

0.395
0.188
0.516

0.009
0.000
0.075

1.525
1.341
1.729

1.233
1.136
1.310

0.002
0.000
0.006

0.030
0.020
0.042

3.968
3.954
3.980

0.77
0.69
0.86

P1N 82054

1T

mean
min
max

1.713
1.607
1.798

0.020
0.000
0.053

0.509
0.441
0.612

0.004
0.000
0.020

1.512
1.429
1.577

1.242
1.207
1.285

0.001
0.000
0.004

0.023
0.019
0.030

3.975
3.966
3.981

0.76
0.71
0.79

P1N 40571

2H1(+2H2)

mean
min
max

1.863
1.792
1.924

0.307
0.302
0.310

0.066
0.063
0.068

0.000
0.000
0.000

1.527
1.418
1.666

1.236
1.167
1.291

0.000
0.000
0.000

0.009
0.007
0.010

3.991
3.990
3.993

0.76
0.71
0.83

The presence of minor Cl in cronstedtite has been alreadyknown, e. g., from Pohled (Hybler et al. 2016), Chyňava
(Hybler and Sejkora 2017), Nižná Slaná (Hybler et al.
2017), or Ouedi Beht (Hybler et al. 2021). Detectable
contents of other elements were recorded only exceptionally (Al ≤ 0.08 apfu, S ≤ 0.01 apfu).
The chemical composition of the allotwin of 2H 1(+2H2) polytypes (Tab. 3) differs significantly from thedata of predominant 1T polytype (Fig. 6), especially by
low Mn (0.06–0.07 apfu) and Cl (0.01 apfu) contents andan elevated content of Mg (up to 0.31 apfu). Calculated
x-values in the range of 0.71–0.83 correspond to data of
1T polytype. Similar chemical composition was deter-236

mined for 2H2 + 2H1 polytypes in the central part of acronstedtite sample from Ouedi Beht (Hybler et al. 2021).

5.3. Cronstedite mineral association
Besides cronstedtite, sporadic carbonates and silica minerals replacing cronstedtite along the cleavage planes
were recorded in fragments of cronstedtite used for thedetermination of polytypes (up to 0.2 mm in size). Carbonates, classified chiefly as siderite (Fig. 7), are chemically very heterogeneous among the individual samples(Sd 48–93Rds 0–38Cal 0–29Mgs 0–23). Rhodochrosite (Rds 97–98
Sd2–3; in sample P1N11848 only) and calcite (Cal81–96Sd3–17

Cronstedtite from Litošice

Fig. 7 Variability in the chemical composition of carbonates. a – plot Fe–Mg–Mn. b – plot Fe–Ca–Mn. The grey arrows indicate a general trend
during the crystallization of carbonates. Note that calcite and magnesite data are not included in figures a and b, respectively. Abbreviations inlegend: LC – layer core, LM – layer margin, VC – veinlet core, VM – veinlet margin.

Mgs0–2; in samples P1N74127 and P1N11848) are less common than siderite. The minimal and fragmentary data due tothe small size of these samples preclude any detailed interpretation of evolution during crystallization of carbonates.
The sample P1N74127 was selected for a detailed
study of cronstedtite mineral association. It is formed by
the symmetrically zoned vein about 1.5 cm thick. The
vein consists of carbonates, cronstedtite, apatite, quartz,
opal and pyrite. Zoning of the vein suggests repetitive
open-space crystallization of main minerals, including
Fe–Mn carbonates, opal and cronstedtite. The primary
texture of the vein filling was modified by the processesof metasomatic replacement, especially around the central
part of the vein.
Quartz and rhodochrosite, developed in the form ofhemispherical aggregates with a layered texture definedby alternating layers of both minerals up to 0.5 mm
thick (Fig. 8a), represent the early phases of the veinparagenesis. Quartz typically has a drusy character, being
present in well-developed isometric crystals. Fine-grained
rhodochrosite is chemically almost pure and exhibits nozonation in BSE images.
The remainder of the vein filling is composed ofcarbonates, cronstedtite and pyrite and contains several
intercalations of opal instead of quartz. Opal typicallyforms botryoidal aggregates (Fig. 8b) and commonly
also fine impregnations in the associated carbonates,
as elevated Si contents indicate it in many of the WDS
analyses (Tab. S2). Opal is chemically mostly pure, although the elevated contents of Fe, Mn and Mg in someanalyses indicate an admixture of carbonates.

Cronstedtite forms two bands, each of about 2 mm inthickness, situated close to the central part of the vein andmutually separated by intercalations of Fe–Mn carbonate
and opal (Fig. 8b). In BSE images, no chemical zoning
was observed in cronstedtite aggregates. Cronstedtite ispartly replaced by Fe-Mn carbonates along grain boundaries and cleavage planes (Figs. 8b–c). The intensityof this replacement increases towards the center of thevein, where apical parts of a younger cronstedtite layer
are entirely replaced by aggregates of Fe–Mn carbonatesand opal (Fig. 8d).
Cronstedtite and opal layers in the younger portionof the vein filling alternate with carbonate layers. Carbonates are dominated by siderite and rhodochrosite(Tab. S2), which exhibit similar texture and fabric in
individual layers. The early massive fine-grained matrix
typically evolves into elongated randomly oriented andmutually inter-grown branchy aggregates in the apicalpart of the layer (Figs 8b, e). The remaining open spacein these porous parts was later wholly filled up by opalor pyrite (Fig. 8e). In BSE images, brighter cores ofindividual branches are rimmed by a darker outer rim(Figs 8b, e). Chemical composition evolves from rhodochrosite (Rds74–99Sd1–25Mgs0–1Cal0–4) to a chemicallyheterogeneous Fe/Mg-richer carbonate, which can beclassified as Fe-rich rhodochrosite, Mn-rich siderite, siderite and/or Mg-rich siderite (Rds10–77Sd20–87Mgs2–26Cal1–3;
Fig. 7). Identical chemical evolution is also observed foranother morphological type of Fe-Mn carbonates present
in thicker veinlets cutting and replacing cronstedtite (Figs8b–c): a center of the vein is formed by rhodochrosite

237Jiří Hybler, Zdeněk Dolníček, Jiří Sejkora

Fig. 8 Mineral paragenesis and texture of vein fill of the sample NM74127 on BSE images: a – the oldest portion of the vein fill, composed of finelayers of rhodochrosite (Rds), quartz (Qz) and minor pyrite (Py). b – branchy aggregates of rhodochrosite (Rds) overgrown by botryoidal opal (Opl)and followed by a thick layer of cronstedtite (Cro). The remaining open space in cronstedtite aggregate is fulfilled by pyrite (Py). Cronstedtite is
weakly altered by siderite (Sd) along cleavage planes. c – example of more pronounced alteration of cronstedtite (Cro) by carbonates (Rds, Sd).
d – youngest part of younger cronstedtite layer close to the center of the vein. In the central part of the figure, there is a cronstedtite grain which
was entirely replaced by opal (Opl) and siderite (Sd), with still well visible cleavage planes of original cronstedtite in the pseudomorphosis. In
the right part of the photograph, there are still preserved relics of cronstedtite in the carbonate matrix. e – growth zonality of branchy aggregatesof Fe–Mg carbonates (Rds – rhodochrosite, Sd – siderite), surrounded by opal (Opl) and cut by younger veinlet of magnesite (Mgs). f – radial
aggregate of apatite (Ap), partly replaced by rhodochrosite (Rds) and overgrown by botryoidal opal (Opl) and early cronstedtite layer (Cro). All
photographs taken by Z. Dolníček.

238

Cronstedtite from Litošice(Rds66–93Sd6–32Mgs0–9Cal1–-6), and both margins by siderite
to Mn-rich siderite (Rds5–36Sd41–92Mgs0–18Cal1–17; Fig. 7).
By contrast, very thin veinlets are formed by siderite
only. The textural evidence suggests that rhodochrosite
was formed by crystallization in an open space (i.e.,
cementing open crack/fissure), whereas siderite originated by the replacement of cronstedtite. Thin veinlets
of Fe-Mn carbonates are often present also in opal,
but without signs of metasomatic replacement of thishost mineral (Fig. 8e). Because of broad textural andchemical similarities/variations, the mutual temporal
relationship of both major morphological types of FeMn carbonates (primary precipitates in layers versus
veinlets/replacements) remains unresolved. Magnesite(Mgs81–82Sd11–12Rds6Cal1–2) is a very rare carbonate. It
forms either irregular small grains enclosed in opal,
small overgrowths on Mn-rich siderite, or tiny veinlets inopal and primary layers of Fe-Mn carbonates (Fig. 8e).
The general geochemical evolution during individual
episodes of carbonate crystallization is uniformly characterized by the elemental sequence Mn → Fe → Mg
(Fig. 7a). The Ca-richer (>8 mol. % of calcite molecule)carbonates are very rare, recorded only in a single spatially restricted domain.
Pyrite forms a filling of the remaining open space orveinlets in aggregates of cronstedtite and the primary layers of Fe-Mn carbonates. It predates veinlets of Fe-Mn
carbonates replacing cronstedtite (Fig. 8c). Chemically, it
does not contain admixtures at levels detectable by EDS
spectra of the electron microprobe.
Apatite was observed only once. It forms a radial
aggregate 0.4 mm in size predating an early layer ofcronstedtite. The aggregate is overgrown and partly also
consumed by Fe-Mn carbonates (Fig. 8f). WDS analyses
showed significant admixtures of S and Mn and highcontents of F (Tab. S3). A systematic deficit of elementsin the position of phosphorus suggests the presence ofelevated contents of CO2 (Tab. S3), implying that thestudied phase is carbonate-rich fluorapatite. Low analytical totals (97–98 wt. %; Tab. S3) may be associated withincreased porosity due to the mechanism of formation ofthis mineral phase: specifically in the low-temperature
sedimentary environment, there is presumed that crystallization of apatite would be a long-lasting process.
Initially, an unstable gel-like non-stoichiometric calcium
phosphate precipitates, which subsequently matured bywater loss and stabilized by sorption of F and CO3 anions
during interactions with circulating pore waters, giving
rise to crystalline carbonate-fluorapatite (e.g., Slansky
1986; Froelich et al. 1988; Stalder and Rozendaal 2004).
Therefore, low analytical totals may be associated withfine porosity originating during the loss of water from theoriginal gel-like substance.

6. Conclusions
The study represents a contribution to our systematic
research of polytypism, chemical composition, and mineralogical association of cronstedtite, with a larger focus
on Czech and Slovak localities.
The polytype 1T (subfamily C) is the most abundant in
the samples studied. The allotwins 1T+1M (of subfamilies
C+A) occur rarely, but they represent the first known
examples from the natural terrestrial environment. Previously they were reported from the synthetic run productor meteorite (Müller et al. 1979; Hybler et al. 2018).
Disordered allotwins of C+A subfamilies were observed
for the first time. The polytype 2H1 allotwinned with asmall amount of 2H2 of the D subfamily is common in
many localities but in Litošice occurs rarely. Although thechemical composition of cronstedtite from other localities
is usually uniform inside the occurrence, in Litošice, asignificant difference was recorded: The subfamily C
crystals are relatively rich in Mn (0.2–0.6 apfu) and poorin Mg, while the subfamily D crystals are rich in Mg (0.3
apfu) and poor in Mn (cf. Tab. 3).
The studied cronstedtite is a part of the symmetricallyzoned hydrothermal vein cutting pyrite shales and is associated with abundant Fe–Mn carbonates (rhodochrosite, siderite), opal, quartz, pyrite, and minor magnezite,
calcite, and carbonate-fluorapatite. The Fe–Mn carbonates, opal and quartz undoubtedly occur in multiple
generations. The textural features, mineral assemblage
and chemical composition of vein minerals suggest low
temperatures of vein formation. Nevertheless, intense
metasomatic replacement of younger portions of cronstedtite filled by opal and siderite was widespread in thestudied vein. A distinct unified chemical trend (Mn → Fe→ Mg) was observed during each episode of crystallization of carbonates.
Acknowledgments. The first author (JH) thanks late Lubor Žák for providing a part of samples of cronstedtite
used for this study. Valuable discussions with SlavomilĎurovič are highly appreciated, too. Comments andsuggestions of two anonymous referees allowed us to
improve the manuscript. We thank Libuše Jilemnická
and Jana Kotková for critically reading the text. JH acknowledges the project 18-10504S of the Czech Science
Foundation and CzechNanoLab Research Infrastructure
supported by MEYS CR (LM2018110). This work wasalso financially supported by the Ministry of Cultureof the Czech Republic (DKRVO 2019-2023/1.II.c,
00023272) to JS and ZD.
Electronic supplementary material. Supplementarymaterial consisting of electron microprobe data for239Jiří Hybler, Zdeněk Dolníček, Jiří Sejkora

cronstedtite, associated carbonate minerals and apatite
are available online at the Journal website (http://dx.doi.
org/10.3190/ jgeosci.335).

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